First of all, conventional insert nut and insert t-nut are briefly explained, which were developed by the same inventor as the present invention, as disclosed in JP laid open patent publication No. 2004-211778. A conventional insert nut 101, as illustrated in FIG. 45 and FIG. 46, has prepared as follows: A metal material is formed into a cylindrical shape having a predetermined length. Then, the internal surface is subjected to a screwing process to form a female screw 102. That becomes a shank portion 103 which is in the form of hallow with a female screw 102 thereinside. Further, the outside surface of the shank 103 (the whole of the outside surface) is covered with a synthesis resin to form a resin layer 104. The outside surface of the resin layer 104 is provided with projections 105 continuously patterned.
Also, another conventional insert nut 106, as shown in FIG. 47 and FIG. 48, is described, which has a shank 103 similar to the example as explained above, having a female screw 102. The outside of the shank 103 is provided with a resin layer 104 made of a synthesis resin, forming projections 105. Also, a flange 107 is formed integrally with the resin layer 104 by a synthetic resin. At the center of the flange 107 made of a synthesis resin, a hexagonal hole 108 is provided for engaging with a hexagonal wrench.
Also, a conventional insert nut as shown in FIGS. 49 and 50 has a shank having a structure similar to the insert nut 101 (106) as explained above, and a flange 110 integrally formed with the shank by using a metal material. The flange is extended outwardly from one end of the shank 103. The outside surface of the flange 110 and the shank 103 is covered with a resin layer 104. The outside surface of the resin layer 104 has projections 105 formed.